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Zhang Heng (張衡)
Chinese astronomer, mathematician, inventor, and poet. Born: 78 AD in Nanyang Died: 139 AD in Luoyang Perhaps the most famous scientist of Imperial China, Zhang Heng left a legacy in many fields. He was a celebrated literary figure most famous for his fu (rhapsodies), a form of semi-poetic literary prose. Zhang is best known for his many inventions and astronomical accomplishments. He expanded the hun-tian cosmological theory to explain many celestial phenomena. Zhang mapped of the heavens and the Earth, employing more systematic methods compared to his predecessors. Discoveries Astronomical Theory In his work Ling Xian (靈憲), Zhang Heng supported the hun-tian cosmological theory of Luoxia Hong (c. 156 - 87 BC), which states that the Earth is a sphere that lay in the center of a vast spherical universe, whereby all celestial bodies traverse in a fluid-like medium. He also explained how moonlight is the reflection of sunlight off the moon's surface, and how solar and lunar eclipses work. Star Catalogue Zhang Heng compiled a star catalogue of 2500 stars. According to folk legend, he counted the stars in the night sky as a child. Approximation of pi Zhang Heng used two approximations of pi: : \pi = \sqrt{10} : : \pi = \frac{365}{116} The method for obtaining the first approximation is uncertain. The second approximation, mentioned in the Ling Xian, was influenced by astronomical data. Inventions Seismometer Zhang Heng invented the world's first seismometer and named it the hou-feng di-dong yi (候風地動儀). The urn-shaped device was designed to detect the direction of seismic tremors in eight directions. It is theorized that the interior apparatus consists of an inverted pendulum that tips in the direction of a detected earthquake, which triggers the mouth of a dragon to drop a metal ball into the mouth of a frog. Water-powered Armillary Sphere The armillary sphere was invented in China since the 2nd century BC. Zhang Heng improved the design and employed waterwheels to rotate the device. Striking Odometer Zhang Heng is credited for inventing the striking odometer, a cart with gears that make puppets strike drums and gongs at different intervals of distance. South-pointing Chariot The south pointing chariot is a mechanical chariot with a mounted figurine that points in one direction regardless where the chariot is moved. The direction is continually corrected to point south using a differential gear. Map Grids Zhang Heng is credited for introducing rectangular grids for scaling physical distances onto a map. His work influenced the research of surveying and cartography by later cartographers like Pei Xiu (c. 224 - 271 AD). Literary Works Aside from his scientific works, Zhang Heng was also an accomplished poet. Many of his poems and rhapsodies captured the spirit of society during the Eastern Han dynasty. His most notable literary works include: Poem of Four Sorrows (四愁詩) Rhapsody of the Western Capital (西京賦) Rhapsody of the Eastern Capital (東京賦) Rhapsody on Contemplating the Mysterious (思玄賦) Rhapsody on Returning to the Fields (歸田賦).Category:Ancient Scientists Category:Science and Technology in East Asia